Our brains take a rather different approach to cores, clock speeds, and parallel processing, however. They operate at variable clock speeds between 5 and 500 Hertz. No Giga here, or Mega or even Kilo. Brain waves, whose relationship to computation remains somewhat mysterious, are very slow, ranging from the delta sleep waves of 0-4 Hz through theta, alpha, beta, and gamma waves at 30-100+ Hz which are energetically most costly and may correlate with attention / consciousness.
On the other hand, the brain has about 1e15 synapses, making it analogous to five million contemporary 200 million transistor chip “cores”. Needless to say, the brain takes a massively parallel approach to computation. Signals run through millions of parallel nerve fibers from, say, the eye, 1.2 million in each optic nerve, through massive brain regions where each signal traverses only perhaps ten to twenty nerves in any serial path, while branching out in millions of directions as the data is sliced, diced, and re-assembled into vision. If you are interested in visual pathways, I would recommend Christof Kochs Quest for Consciousness, whose treatment of visual pathways is better than its treatment of other topics.